Dinos Neither Hot Nor Cold, according to articles in BBC News and Nature News 12 June 2014, and Science vol. 344, p1268, DOI: 10.1126/science.1253143. There has been an ongoing debate over whether dinosaurs were cold blooded, like living reptiles and amphibians, or warm blooded, like mammals and birds. Cold blooded animals are more correctly called ectothermic, meaning they gain heat from the external environment, usually by basking in the sun or on warm rocks. Warm blooded animals are called endotherms, meaning they heat their bodies from within, by burning food to produce heat. Being warm blooded enables animals to keep their body temperature at a constant level, higher than the surrounding environment, and also enables animals to grow at faster rates, and maintain a high metabolic rate in order to keep active throughout the day (and sometimes night). Because dinosaurs seemed to have a high growth rate in their early years some scientists have suggested they were warm blooded. However, other scientists have pointed out that maintaining a high body temperature requires much more food, and animals the size of dinosaurs would not be able to get enough food to sustain them.

John Grady, a biologist at the University of New Mexico in Albuquerque, has come up with a new theory that may solve this dilemma – dinosaurs were somewhere in between, and could be called “mesotherms”, i.e. being able to boost their body temperature from within, but not maintaining a steady high temperature all the time. Since there are a few living animals, including tuna fish, some fast swimming sharks, leatherbacked turtles and echidnas (Australian spiny anteaters) that regulate their body temperature this way, this is not a completely far-fetched idea.

To test this theory Grady and his colleagues carried out a survey of growth rates and body size in 381 different species, including 21 dinosaurs, using these as an indicator of metabolic rate. Grady explained: “If you double your metabolic rate, you roughly double your growth rate”. He then compared the growth rates of dinosaurs with known cold and warm blooded animals, as well as the known in-between ones, and found that dinosaurs fitted into the “mesothermic” range.

The research team suggest being mesothermic enabled dinosaurs to be more active than large reptiles like crocodiles, but without needing as much food as similar sized mammals would need. Robert Eagle, a geochemist at the California Institute of Technology, Pasadena agrees with this idea. He commented: “In a world that was generally hotter than today, it wasn't really necessary to be a full endotherm”.

Editorial Comment: Grady’s mesotherm theory and Robert Eagle’s comment about the environment are probably close to the truth, and provide another reason why dinosaurs have died out. So let’s look at these findings in the light of Biblical history. In the beginning the world was created “very good” with a pleasantly warm climate much more uniform than today. Therefore, animals could maintain their body temperature more easily, and in a lush environment with plenty of nutritious plants to eat, very large mesothermic animals, who only needed to fire up the internal furnace on a part time basis, could stay active and get enough to eat. However, after Noah’s flood when God warned Noah that winter and summer were coming, the environment rapidly degenerated, extremes of temperature came into the world, and animals that were both large and metabolically active would have a hard time surviving.

Also, the sex of sauruses, such as crocodiles in the present, is often determined by the temperature their eggs are incubated at. So a world where winter became an increasing problem by Job’s day when the Bible reports ice, then the larger saurian reptiles would have grown up monosexual, and extinction was sure to follow.

Note also Robert’s Eagle’s comment about the world being hotter in the past. What does he think heated it up – obviously not people driving cars and generating electricity. (Ref. thermoregulation, metabolism, physiology)